Process for obtaining pectin and citric acid from their source materials



Dec. 4, 1951 G. M. COLE 2,577,232

PROCESS FOR OBTAINING PECTIN, AND CITRIC ACID FROM THEIR SOURCE MATERIALS Filed Feb. 17, 1947 V I ICRUSHING OR GRINDINGI 2 SCREENING Junc PULP 3 COMMINUTING (IF DESIRED) I WATER (IF DESIRED) I 4 DIGESTING I- Ls I FILTRATION PULP CLARIFIED JUICE LIQUOR 6 CATION SORPTION (IF DESIRED) I ACID SQRFT'IDN STRONG ACID (H2SO4)+ I AmofiTEx EHANcE crrR|c ACID LIQUOR I PRECIPITATION OF PECTIN LIQUOR I CONCENTRATION I v METAL SALT (AICI3)) 8 PECTIN WITH METAL CRYSTALLIZATION HYDROXIDE CITRIC ACID 9 'SQ ZQI LW E |scARD FILTRATE METAL- PEc-IIN COMPLEX PECTIN INVENTOR:

ON MANLEY COLE h BY M ATTORNEY Fatented Dec. 4, 1951 CITRIC-AGID FROM THEIR soURoE MATERIALS: Gordon aiiley ole, Corona; Califi, assignor to California; FruirGr owers Exchange, Los An- A iicaueiiii' bifia fyi7;- 1947, serial Nb. teams" Thisinvention relates to new methods for-the manufacture of pectin and citric acid. 1 More specifically the invention relates to a process for the manufacture of pectin whereinthe pectin -is'ex tracted from its source materials by means of an aqueous solution containing citric acid, and wherein the'citric acid isthen removed from the extract .and the pectin is'subs'equently pre'cipi tatedfrom the de-acidified extractby means of metallic compounds;

It is accordingly an object of this invention'to provide a combined process for the'recove'ry ofpectin and citric acid from either a single natural source material, or a plurality of source mate-' rials.

A further object of the invention is to provide a method for preparing? pectin whereby the pectin may be extracted: from its source mate rial by means of an aqueous citric acid solution:

and precipitated by means of a metallic compound;

Another object of the invention is to provide a directmethod for recovering citric acidfrom a liquor or fruit juice containing pectic mate rials and citric acid.

Other objects and advantages of 'my process will be apparent to those'skilled in the artzas the invention is more specifically disclosed hereinafter.

The invention may be more readily understood by reference to the drawing, which shows a flow sheet which is a diagrammatic representationof a process'comprising the main features ofthe invention. In the detailed description which follows, reference will be made to the steps outlined in the flow sheet.

EXAMPLES 5 Claims. (o1. 260209.5)

pressed pulp through" ail-ordinary screw type of" grinder (step 3). A-grinden withinch'holes in-the face plate yields a satisfacto'rily con'i minuted pulp. These operations and th'e equip" mer t for performing them may bemoreor'less conventional and need not-be described with-"any particularity. They are carried oil-under any convenient plant operating conditions and at prevailing temperatures. p v

The finely ground pulp is then remixed with its normal complement of lemon juicejresulting' in'a thick slurry (Step4). For this -Iempl0yany 2 senate-tam referoneeduipped 'with -aii' ag itator of. we tespeed; thatzthe' entire dige tion' batch-may be ade uately agitated, in 0rd" measure? good extractions. To? this, 1 add" a'boiit' s volumes of watrifor one vo1u'me.'of'juice:: results in an extraction or digestion batch itsli'q'iior havinga pH of "about- 3.0. I then ag'itatetlie': mixturelof l dilute lemon juice and" pulp for about '60minutesiat1about e. (step D1 of the" vario usi means common in' this art for heating may be employed;

"At the end; of: the; extraction" period" the juice eiitracttisfseparated from'thetpulp by first 'draine ing orireelingto remove the coarser pulparticles and then 'filtering thealiquid port-ion to remove the finer pulp-particles: (step 5) In order to illustrate at this point, and follow-' in'gg: some of the characteristics :of: these procedures; as well as to exhibit: some; modifications ofr the same, Imwill give -hereinbelow in- Tables LII;- and-III complete cletails "of: threeextract-ions preparedby procedures closely like. the: above"; wherein-for the-first steps, thespecificcoriditions of extraction -and-the,composition of the extractswere" asset forth-in Table-I, which follows:

Table I Extratioii'Batch N01 1' '2 g 4.0- 0 '4f9- x r p i i me- EttratidriTifiie' (MiriL) '60 '90 nH 3.0 3.0 '31 Filtered Extract Vol., Liters per kg. pulp 3. 2 2. 6 5. Pectin 00110., Gramsg er literpr. 4. 6 7.4 4. Citric acid, Grams per liter 8. 8 l2. 0 8.

After' performance of; step 5 the-juice v ex; tract is. readyvto be trea d for the removal oi" citric acid. This is? done'by passing the extract seriallythrough. a hydrogeneirchange material ions';i-I*igive below inidetailithearesults' obtained- 1 when the lemon *juice pectin? extracts prepared" as set forth in Table I were percolated through" bdsOf a resinous. cation -"sorbing material (step 6). More; specifically,-- the? cation: sorbiiig :m'a-rteria'ls :"were of the'hydrogen zeolite typerwhicli are'capable' of' exchanging-a hydrogen :iorifora metallic ion: The"- specific-conditions as well as the results of the procedures employed are set forth in the following table:

column. The last portions, which contain con siderable sulfuric acid and little citric acid, are used at the beginning of the next run. In this Table H manner an efiiuent is obtained which upon concentration (step 12) and crystallization (step 13) Batch 1 2 3 yields practically pure citric acid.

, It was found that the citric acid liquors reinhttiifhfi ftfiatttiitiiif?fifff."":: i1? 3: s 112 9 e m a total or about of the Efiluent Ash, Grams per 1iter 0.23 0.24 0.4 citr c acid contained in the efliuents from the Ash Sorbed, Grams per liter ofbed vol 6.0 13.6 14.7 lo cation sorben The procedures I have outlined above are given calculated as Caco" as examples and should not be interpreted as The efliuents obtained from the cation sorber iti the scope of my invention. Various (Table II) were then percolated through beds of mgdifications may be made throughout t a resinous acid sorbing material ep 'v- The 1,; process, as will be obvious to those skilled in the liquors we e perco a until substantially ll of art. Some of these possible variations will be the citric acid had been removed. Tests indih reinafter t, t cated that the percent of citric acid, as anhydrous, remaining in the efliuents after acid sorp- GENERAL CONSIDERATIONS tion amounted to less than about 0.03%. This In nearly all methods for preparing pectin corresponds, in a liquor of these particular charwhich are now in use, the pectic source material acteristics, to a pH of about 5.5. The liquors besuch as citrus peel or apple pomace is treated fore acid removal contained an average of about and extracted with an aqueous acidic solution. 1% of citric acid. This treatment solubilizes a major portion of the It should be noted. that a pH of 5.5 is abnorinsoluble pectic materials which are naturally mally high for pectin liquors and hence, it it present in the source material. The acidic aqueis desired to store such liquors for any length ous extract is then treated to precipitate the pecof time, they should be slightly acidified, say, tin. This precipitation has been accomplished to about pH 3 or 4 with an acid such as hydroin the past in a number of different ways. For chloric. instance, the pectin may be precipitated by the The three pectin liquors obtained as effluents addition of alcohol. This process is expensive from the acid sorption step (step 7) were treated and, in addition, does not produce a pure pectin, by addition of aluminum chloride solution in but one which may be and usually will be conquantity suificient to precipitate pectin, and then taminated with other alcohol precipitable conwith a suitable quantity of a 15% soda ash solustituents of the source material, such as proteins. tion to bring the liquor back up preferably to 21. Another process involves the precipitation of pH of 3.8 to 4.0 at which point precipitation 00- pectin directly from the extraction batch by adcurs (step 8). The precipitates were filtered dition of a metal salt which hydrolyzes in the (step 9), ground, and washed with alcohol acidiaqueous medium to form a colloidal hydroxide. fied with hydrochloric acid (step 10). These 49 This colloidal hydroxide, according to present steps are performed in the usual way, by known theories, fiocculates the pectin, which is premeans. cipitated as a gelatinous mass. The method is The dried products consisted of pectin of norgenerally preferable to and more economical mal appearance and properties. The results of than the alcohol precipitation process. I have these procedures are tabulated in the following found, however, that this precipitation with a table: metal salt such as aluminum chloride or alumi- Table III N 00 H 0 A16] on 0 i 21 s tt at 3.1, a. 2, wase.pp. eing i a ear" seat.) 59%?! g./l. Grade Ash and moisture free.

The pectin prepared by this method is comparnum sulfate is remarkably sensitive to citrate able in nearly all respects to the pectin prepared 0 ions. The citrate ion apparently forms a soluble by sulfurous acid extraction of citrus pulp. The or dispersible complex with the aluminum salt, setting time is that of a normal rapid set pectin; which complex is stable and is not effective to the texture of the jelly is good or average in most precipitate pectin. This is the reason it has cases and the jelly grade is high. been, empirically, the practice to avoid, as far as Citric acid extracted pectin may be further 5 possible, the occurrence of citric acid and citrates treated with acid, to produce a slow setting pectin, in the extraction batch when this method was to or may be treated with alkali or otherwise to be utilized. produce a low methoxyl pectin which is capable The disadvantages in endeavoring to avoid the of jelling an aqueous medium in the absence of citrate ion are, however, at least threefold: (1) sugar. 70 Citrus source materials always contain some citric The citric acid was displaced from the charged acid or citrates which must be eliminated, as far acid sorber beds with 5% sulfuric acid (step as possible, by an extra purification step before 11). The citric acid effluent was collected in each the precipitation of pectin with a metal salt. run until tests upon fractions thereof indicated This is usually done by a water washing of the that no citric acid was being displaced from the source material prior to the acid extraction of been known prior hereto that is capatle oi re moving citrates as completely as I have now established would be desirable. I (3) Citric acid is actual-1y an advantageous extractaht for insdlubl'e natural pectic materials; When itwas believed that citrat ion had to' be" avoided in; the process, a strong acid was used: in-the extract cn: ste'pgs'dch as-sulphurous or hydrochloric acid, the anion of which did not interfere with the rarecipitation step. While these acids-will rapidly sb'lubilize and extract-pectin from pectic soiir e materials, they also have a's'trong te'ndencyto ldw'erth'e j'elling sewer or grade of the pectin. Qi'tri c acid, on the otherhand; will sol 'ubi-lize the a ndyi n addition; yields a pectin of very high-jelly grade; It is; therefore, highly advantageous to use citric acid in the extraction step; .Now, at the same time, its disadvantageous results in the pie pita'tionstep are overcome. By iiiy imprcved' process all of the boveuma vamagesare overethic; there is no need for separate washing steps tit-remove citrate ions-from the source material, the it is not necessary touse strong acids such as sulfurous or hydrochloric.

Another advantage of my process lies in the almost complete recovery of citric acid in pure form; which ismade; possible; uln the citric a cid field a" method has long been sought whereby pure citricacid could beobtainedhy direct crystallization from lemon juice. I Commercialv methods now in use require longstorage'of the iuicetc permit enzymic decomposition of the 'gummy pectinous materials. neutralization of theatermented liquor with lime to producev calcium citrate, recovery of the latter by filtration de,-- composition of the. calciumrcitrate with. sulfuric acid to produce calcium sulfate. and pitricacid liquor, and finallyp'urificationoi the liquor and crystallization of the citric acid therefrom, Ac: cording to my process pure citric acid is produced without the necessity for any ofllth'e above steps other than the final crystallization; v

teammates Ate Anti-leaflets l fsource 'n'l aterial's'jolf. will be f ofi'n'd- 6 st of various nat v 1n and citric acid. Ge eiallyit ti v my process is best adaptedf or'u a ties wher'ea 'sourcie'of pectin and a s ourceof c; metre brought tc ageth'er, us'u'allyl' p v ties in the peel and pulp r citrus fruit apples, and insziialler quantities sug s and pineapple. Thec'itrusirjuits' andpineapp s gis contain cori's'i er "quantitie'sofcit or pectin, and sugar beets Jar only s me of i 11 iri "fr .e t 'trl @619 flier-i1 6 e e e er iieae $61,! W c ee t fif en flbibetti 'P' 'e ne acid to ma h nr ee e nem ee'l,

is not essential that the citric acid and pectin qt crieina e n thes me-re cmet fiki Qen-era y ,i m ybe. st ed hat. h ltii e t ta l hoi ev o so c mat a licrlbct pe t n nd tric acid .e.sts..;1 ely up n-co sidera ions l i ecc c v, Bu ly, rom th li hepreti at stands point, however, it is clear that any pectic source pectin almost as efficieritly as a; strong acid I St?! 1 Instead of the crushing or grinding specifically employedcinlthis step; any equivalent procedure for effectively freeing the juice present within the starting or source materialymay .be sub: stituted. For example; when working withcitrus, fruit; 9; reaming or lourringoperation whether performed mechanically or by hand, serves ad: niirably to freethe juice; Other types of devices perform. equivalent functions.

Ste'ib 2 a y, pe, at i e ail ieea'ee tepsi fi ir .c.,.s v el n nn.v r,i e mec ani a riyances ensep ret n h Juice re titr frcmthe ee in ludineth a m lb freemi ma hressu' e'l' r e he vm e is, h a eetiey ule x is har e at one p te fr m. the ma h n a her e eth r:. vWhe e a e ate e e we of the juice is provided for, sucha device may be made to perform both step 1 and step 2.

Step '3. v as notessenti tl. th t ifi jtnlp ib fi i e i tidbit. but. I navei u that e n extr ction tp qeeed I more rapi ly a d e et tly i it u p ra er finely ground, thus p in S1 29$1P4if lt c. 11 1 11 to he jui edy l etx in e iei accomn h nsz his resul Wil y q t0 f Q SQP-i skilled in thi a t. o e e ents! hi h; de tei to diretatten iqn i .e m riee e entially i twds s, in er e of. c ose y s aced ut me wheel or s ws-T ee ope ate cl th d uce. prcd l r om it s peelr at in processing citrus fruitit may be foundthat more pectijc source material becomes available vthan can be extractedwith the citric acid avail:

able fromthat source material. In this casethe citric acid liquors recovered may be recycled to thepxtraction step andagain used to extract pectin from fresh source material. By operating in this manner pectin may be extracted iron; source materials originally containing little or nocitric acid. On the other hand; if it is found desirable to recover the citric acid as it is displaced from the acid sorbing material, the d ficien ye citric acid in he r w mat riel 1h y be made up byad in an ther c d e ch .-e. suliuriahydrochloric, or'sulfurous acid toe rry out the extraction. If such an acid is used it will so be so l n with thee r ecid. at

gained thereby do notwarrant the expense, and, furthermore, the fullobject of my invention will not be achieved thereby. For this reason, I

prefer to use citric acid in a crude or unpuriiied or partially purified form, such as would ordinarily be discarded or separately refined to obtain the citric acid. Such materials include, for ex-..

Fre-

ample, lemon juice or pineapple juice. quently such juices are used as a source of .citric acid only when they are of such quality as not to be suitable for beverage purposes. I. have found that this type of juice may very suitably reason that, in a mixture comprised of the comminuted pulp of lemon with its juice, although adequate acid may be present, the proportion of liquid in such a mixture is ordinarily not great enough to extract the pectin with maximum efficiency. Thus it will be seen that some dilute citric acid juices or liquors may be of such strength as to be suitable for use directly. Other more dilute citric acid liquors, which may not be of sufilcient strength for this purpose or from which it is ordinarily not economically feasible to recover the acid, may possibly be supplemented with a stronger juice or liquor, or with acid, and used as the extractant.

The juice which has been expressed from the pulp in step 1 of my process may, if desired, be treated to remove and recover the essential oil before it is remixed'with the pulp at step 4. When whole fruit is macerated, as in the first step of this process, the essential oil contained in the peel becomes partially dispersed in the form of small droplets in the aqueous phase.

Since the specific gravity of the oil is less than that of the aqueous phase, satisfactory separa-.

tion of the oil may be obtained by passing the juice liquor through a centrifuge. Such a procedure, in addition to recovering the oil as a valuable by-product, also is advantageous in that it eliminates the possibility of the oil droplets becoming deposited upon the cation exchanger or the acid sorbing material, thus reducing the efilciency of these materials and necessitating frequent shutdowns for cleaning.

Satisfactory extraction of the pectin in step 4 is dependent uponseveral interrelated variables. These variables include temperature, time of extraction, pH of the liquor, size of the pulp particles and the degree of agitation employed. The governing principles are that these variables should be so adjusted that a reasonably complete and efficient extraction may be obtained without unduly degrading the pectin. Temperatures above 100 C. will ordinarily not be employed since pectin is rapidly degraded at those temperatures. The most practical temperatures range between about 70 C. and about 100 C. Prolongation of the time of extraction will be found to result from use of lower temperatures, if effort is made to achieve relatively complete extraction. T

The pH of the extraction liquor should preferably be between about 2.0 and about 3.5. At a pH either appreciably above or appreciably below this range it will generally be found that, at any practical extraction time and temperature, the jelling power of the pectin will be reduced. If the temperature and the pH are maintained approximately within the above ranges. the'major part of the pectin will be extracted in from about hour to about 2 hours. The finer the material is ground, the faster and more com-' plete will be the extraction. However, if it is ground too finely, other disadvantageous results may follow, such as difliculty in filtering or separating the pulp particles from the liquor.

Step 5 Numerous suitable means are known by which the residual pulp may be separated from the extraction liquor or juice, and all are within the purview of my proposed procedures.

The yields of pectin and citric acid may be increased by extracting the pulp with further small quantities of water, which may be filtered oif and added to the filtered juice. A procedure which I have found, to be particularly advan; tageous consists in treating the filtered pulp with u about three separate portions of water, the first;

of which is added to the original juice nitrate and the second and third of which are used to make up the first and second washings of a succeeding pulp batch. Such a procedure may be extract from a preceding run. By operating in: this manner, an efficient extraction of pectin may be accomplished without unduly diluting the first juice extract, since. only the second extract need be added thereto.

Step 6 For removing metallic ions, I may use any of the well known materials which are water in-; soluble and are capable of exchanging a hydro-. gen ion for a metallic ion. In particular, I may use the carbonaceous hydrogen zeolites such as. those described in the Transactions of the American Society of Mechanical Engineers for May 1938, pages 315-825, or any of the various phenolic-aldehyde resins or phenol sulfonic acidaldehyde resins. These materials are capable of exchanging a hydrogen ion for a metallic ion even though the percolating solution is already fairly concentrated with acid. I have found thatsolutions having a pH as low as 1.0 are still capable of exchanging metallic ions for hydrogen ions.-

tice to pass the liquor through a bed of the ma'- terial. However, it is not essential that this be done. The important thing is to bring the liquor and'the treating material into intimate contact: This may be done, for example, by mixing the material with the liquor and then removing it therefrom, as by means of screening, reeling, centrifuging, filtering, or the like. Naturally, in any such process due regard must be had of the frangibility of the ionic exchange material.

Whenever in the use of these materials, tests show that substantial quantities of the cations which it is desired to remove are, in fact, coming through in the treated liquor, the treating step with that material should be discontinued. The material may be regenerated and its ability-to exchange hydrogen ions for other cations renewed by thoroughly washing it with a strong acid, as, for example, an aqueous solution of a mineral acid. The material will then be carefully rinsed in order to avoid introduction of the simpcalled.

- :meneratin acidintea subsequent -.acidsorption Step 7 The acidscrbing material used. may be anyof :the well :known anion exchange materials, so

For example, m-phenylene diamineformaldehyde resins, aniline-aldehyde resins, :guanidine-formaldehyde resins, .dicyandiamide resins as well as certain rinsoluble metallic oxides,

:may be used. In general any material which is insoluble under the necessary conditions, and whichwill remove acids from aqueous solution may be used.

The capacity of these acid sorbing materials for citric acid is considerable; in some instances it-may run as high asabout 120 15'0 grams'of citric acid per liter of acid sorber. As the acid extract is percolated through the anion exchanger, the bed becomes progressively saturated with citric acid, with a consequent gradual increase in hydrogen ion concentration of the eiiluent. The eiliuent at the "start of a run will have a 'pH of about 7.0 to 7.5. When the pH reaches about 5.15 it "is desirable to re-nercolate the effluent through a fresh bed of acid sorbing material, if complete recovery of citric acid is desired and for maximum efficiency "of the subsequent pectin precipitation.

.I desire at this point to call attention to an interesting and useful phenomenon. Lemon luiceextracts contain a natural'indica'tor which reflects decreasing pH of the liquor and, hence, this natural indicator may be used to indicate the point at which the liouorshould be recirculated.

the acid sorbing abilityv of the exchanger begins to be used up, the pH of the efiiuent will begin to drop. When the pH falls to about 5.5, a darkening of the liquor is observed. After reaching approximately this point, the pH drops rather abruptly. At about 3.3 the dark color again disappears. For complete removal of citric acid it is desirable to recirculate the liquor soon after it begins to turn dark, preferably through a fresh bed of acid sorber to be used in another run.

In order to obtain satisfactory precipitation of pectin from the deacidified liquor by precipitation with metal salts, it is essential that the citrate ion be reduced toa minimum, and preferably be removed substantially entirely. I have found that, in general, no pectin can be precipitated from liquors containing more than about 0.25% of citric acid, calculated as anhydrous, if normal ouantities of the preci itating salts are used. Even at concentrations of citrate ion as low as about 0.15%, precipitation will, in most cases,

of citric acid or citrate ion is progressive, small quantities causing a slow and incomplete precipitation, and larger quantities preventing any precipitation at all. In general it may be stated that the percent of citric acid or total citrate ion in the liquor must be reduced at least to below about 0.25%, and in most cases preferably to belowabout 0.08%, in order toobtain completely satisfactory recovery of the" pectin actually present in the liquor without using excessive and a f quantities of reagents. Y

The factors which .Step 8 The deacidified juice liquor "from the acid sorber (step 7) consists of a pectin liquor containing little or no citric acidor citrate ion and is usually ready to be treated directly for the vrecovery of pectin. The procedure from this point for recovering pectin from the liquor may be substantially the same as thatset forth in U. '5. Patent No. 1,497,884 to Jameson et al., or preferably, theimprovedprocess setforth'in 01S. Patent No, 2,300,651 .to Cole and Holton. Essentially, the pectin recovery process consists in subjecting the'pectin'liqubr to the "action of a colloid having 'a charge opposite to the charge of the colloidal pectin. The charge on the colloidal pectin is thus neutralized and the pectin precipitates as a 'flocculent 'mas's'together with a small proportionof the precipitating colloid. l

The precipitating agents which; prefer ..to use are those metal salts or compounds which, evenin slightly .acid solution, partially hydrolyze to form a colloidal metal hydroxide having a charge opposite to the colloidalpectin particles. Examples of such salts are the sulfates, acetates, and chlorides of aluminum or iron.

Other heavy metal salts such ascoppersalts,

may also be used, although theirflprecipitating action upon the pectin appears to result from the formation of insoluble metal pectinates instead of the colloidal flocculation which occurs with aluminum or iron salts.

Step"? After precipitation, the pectin-metal complex is filtered, centrifuged, or otherwise separated from the mother liquor, and as much water as desired ispressed from the precipitate.

. Step 10 The complex is washed'with an acidified alco 'holic solution to solubilize and remove the metal hydroxide. The alcohol wash also serves to remove natural coloring material which isusually present in the crude precipitate. Upon'drying and grinding the washed pectiira good grade of pectin is obtained which will produce-a clear,

colorless jelly. V

Step 11 The citric acid may be displaced from the acid sorber with any strong acid such as sulfuric, hydrochloric, or phosphoric acids. Any acid stronger than citric acid may beused. For my purposes I prefer to use, as stated previously, a 5% sulfuric acid solution. Stronger acid soluti'ons may be used, but I have found that the more concentrated acids are not as eflicientin displacing citric acid from the bed as the relatively weak 5% acid. If concentrated acids are used, the efiluent will normally contain a higher proportion of strong acid to citric acid than in the case of a more dilute a'c'id. Of course, if any eifiuent is found'to containundesirable quantities of strong acid, it may be 'percolated as the first liquor through a citric acid charged bed ready to be regenerated. thuseliminating the last traces of strong acidfrom the efliuent.

When all the citric acid has been displaced from the acid sorbing material with sulfuric or other strong acid it is necessary to regenerate the bed witha base. For this purpose-I prefer to use sodium hydroxide or sodium carbonate solution 'as my invention:

StepsIZ and 13 The citric acid liquors obtained by displacement are generally of such purity that they may be'directly concentrated by evaporation, according to known methods, until crystalline citric acid is obtained. The crystals may be of any desired size, depending upon the degree of agitation employed.

If it is desired to produce sodium citrate instead of citric acid, the citric acid charged bed may be regenerated directly with sodium hydroxide or sodium carbonate. In this case the regenerant efiluent is simply evaporated and crystallized to obtain pure sodium citrate.

COMMENTS preferred not to use any of these terms, since in many instances they appear to be misdescriptive. For example the well kown aminealdehyde resins, in their basic form, do not exchange anions; they appear to combine chemically with the whole acid molecule to form an amine salt type of product. To refer to such a reaction as an adsorption of acid would likewise be misleading since this term seems to be restricted to the physical accumulation or occlusion of gases or solutes in thin layers upon the surfaces of a solid. The term absorption, on the other hand, implies a soaking up of the ions or solutes into the interior of a particle. In other instances the exact mechanism by which an anion or cation may be removed is not known.

For all the above reasons I have preferred to use the generalterm sorber in describing the acid or metal removing materials. This term is intended to include" any of the materials which willsorb, or remove from solution, acids or metals, as'the case may be, whether'the mechanism of sorption consists of an exchange" of ions, a'chemical combination, an adsorption or absorption of ions or solute, or any combination of those mechanisms.

Having now described my invention in such full. clear, and exact manner as to enable others skilled in the art to practice thesame, I'claim 1. A process for preparing pectin 'by a citric acid extraction process which com rises digesting comminuted lemon pulp with an aqueous mixture comprising lemon juice. said lemon juice being present in amounts sufficient to extract the pectin from the source material, separating the extract from the residual pulp, passing said extract first through a cation sorbing material capable of removing metallic cations from citric acid solutions and then through an acid sorbing material consisting essentially of an insoluble polyamine resin to remove substantially all of the cit ate ions, and finally treating the extract with a polyval'ent metallic salt to precipitate pectin therefrom in the form of a waterinsolu -le pectin-metal complex.

2. A process for preparing Ipectin which comprises treating a pectinous source material with an aqueous mixture comprising citric acid and soluble salts'thereof, said citric acid being present in amounts sufficient to solubilize arid ex- 'tract the pectinfrom said s'ource material, separating the resultant pectin extract from-T the residual pulp, passing-said extract first through a cation sorbing material capable of removing metallic ions from citric acid solutions and'then through an acid sorbing material consistingessentially of an insoluble polyamine resin to" remove substantially'all of the citrate ions, and finally treating the extract with a polyvalentmetallic salt to precipitate pectin therefromin the form of a water-insoluble pectin-metal complex. 3. A process for preparing pectin-by a'citric acid extraction process which-comprisesjitreating comminuted citrus fruit pulp withan' aqueous mixture comprising citric acid and soluble salts thereof, said 'citricacid being present in amounts suflicient to. extract the pectin from the source material; separating the pectin extract from the residual pulp, passing said extract first through a cation sorbing material capable of removing metallic ions from citric'acid. solutions and then through an acid sorbing material consisting essentially of an insoluble polyamine resin to remove substantially -all of the citrate ions, and finally treating theextract with a-polyvalent metallic salt to precipitate pectin therefrom in the form of awater-insoluble pectinmetal complex. 7 l I v 4. A process for preparing pectin from lemon pulp which comprises digesting .comminuted lemon pulp with an aqueous mixture comprising lemon juice, .said lemon juice being present in amounts sufiicient to extract the pectin from the source material separating the. extract from the residual .pulp, passing said extract first through a cation. sorbing material capable of removing metallicions from citric acid solutions, and then throughan acidsorbing materialconsisting essentially of an insoluble polyamine resinwhereby the percentage of citrate ions in the extract is reducedatleast to below about 0.25%, and finally treating the extract with "a collodiaLfpolyvalnt metal hydroxide to 'precipitate pectin therefrom in the'form of a;wat;erinsolublepectin-metal complex. "Q

5. A process for preparing pectin by a citric acid extraction process which comprises treating comminuted citrus fruit pul p with an aqueous mixture comprising'citric acid and soluble salts thereof, said citricacid being pi'es'entin amounts sufficient to extract th'e'pe'ctin from the source material, separating the pectin extract from the residual pulpjpassing said extract first through REFERENCES CITED The following references are of record in the file of this patent;

UNITED STATES PATENTS Num er Name Date 1,385,525 Doell et al; July 26, 19-21 1,808,737 Loesch June 2,1931 2,253,061 Cole Aug. 19, 1941 2.273.521 Hirsch Feb. 17, 1942 2,323,483 Myers et al. July 621943 2,392,535; Leo et al.. Jan. 15,1946 

1. A PROCESS FOR PREPARING PECTIN BY A CITRIC ACID EXTRACTION PROCESS WHICH COMPRISES DIGESTING COMMINUTED LEMON PULP WITH AN AQUEOUS MIXTURE COMPRISING LEMON JUICE, SAID LEMON JUICE BEING PRESENT IN AMOUNTS SUFFICIENT TO EXTRACT THE PECTIN FROM THE SOURCE MATERIAL, SEPARATING THE EXTRACT FROM THE RESIDUAL PULP, PASSING SAID EXTRACT FIRST THROUGH A CATION SORBING MATERIAL CAPABLE OF REMOVING METALLIC CATIONS FROM CITRIC ACID SOLUTIONS AND THEN THROUGH AN ACID SORBING MATERIAL CONSISTING ESSENTIALLY OF AN INSOLUBLE POLYAMINE RESIN TO REMOVE SUBSTANTIALLY ALL OF THE CITRATE IONS, AND FINALLY TREATING THE EXTRACT WITH A POLYVALENT METALLIC SALT TO PRECIPITATE PECTIN THEREFROM IN THE FORM OF A WATERINSOLUBLE PECTIN-METAL COMPLEX. 